Large vortices with scales ranging from hundreds meters to tens of kilometers are generally found in the atmospheric convective boundary layer(CBL). These vortices play important roles in the vertical transport of mom...Large vortices with scales ranging from hundreds meters to tens of kilometers are generally found in the atmospheric convective boundary layer(CBL). These vortices play important roles in the vertical transport of momentum,heat,water vapor and other tracers in the boundary layer.On the basis of the view of interaction between the convection in CBL and the gravity waves in the upper stable layer the authors developed a convection-wave theory on the formation of large vortices.According to the theory the wavenumber spectrum of the large vortices mainly depends on the atmospheric conditions in both of the upper and lower layers,such as wind speed,wind direction shear,stratification as well as temperature jump. In the present paper satellite image and weather data in a case of cold air outbreak over warm ocean are analyzed to study every stage of the convective processes,such as cloud street, convective cell as well as their transformation.According to the theory the wavenumber compositions for cloud street and convective cell are calculated,respectively,on the basis of the atmospheric conditions at every stage.The distributions of vertical motions,convergent band and disturbed interface are obtained and compared with the cloud patterns in the convective processes. Thus the study seems to offer a likely explanation for the origin of large vortices in CBL.展开更多
The liquid droplet evaporation character is important for not only combustion chamber design process but also high-accuracy spray combustion simulation. In this paper, the suspended droplets＇ evaporation character wa...The liquid droplet evaporation character is important for not only combustion chamber design process but also high-accuracy spray combustion simulation. In this paper, the suspended droplets＇ evaporation character was measured in a quiescent high-temperature environment by micro high-speed camera system. The gasoline and kerosene experimental results are consistent with the reference data. Methanol, common kerosene and aviation kerosene droplet evaporation characteristics, as well as their evaporation rate changing with temperature, were obtained. The evaporation rate experimental data were compared with the prediction result of Ranz-Marshall boiling temperature model（RMB）, Ranz-Marshall low-temperature model（RML）, drift flux model（DFM）, mass analogy model（MAM）, and stagnant film model（SFM）. The disparity between the experimental data and the model prediction results was mainly caused by the neglect of the natural convection effect, which was never introduced into the droplet evaporation concept. A new droplet evaporation model with consideration of natural convection buoyancy force effect was proposed in this paper. Under the experimental conditions in this paper, the calculation results of the new droplet evaporation model were agreed with the experimental data for kerosene, methanol and other fuels, with less than 20% relative deviations. The relative deviations between the new evaporation model predictions for kerosene and the experimental data from the references were within 10%.展开更多
基金This research was supported by the National Natural Science Foundation of China
文摘Large vortices with scales ranging from hundreds meters to tens of kilometers are generally found in the atmospheric convective boundary layer(CBL). These vortices play important roles in the vertical transport of momentum,heat,water vapor and other tracers in the boundary layer.On the basis of the view of interaction between the convection in CBL and the gravity waves in the upper stable layer the authors developed a convection-wave theory on the formation of large vortices.According to the theory the wavenumber spectrum of the large vortices mainly depends on the atmospheric conditions in both of the upper and lower layers,such as wind speed,wind direction shear,stratification as well as temperature jump. In the present paper satellite image and weather data in a case of cold air outbreak over warm ocean are analyzed to study every stage of the convective processes,such as cloud street, convective cell as well as their transformation.According to the theory the wavenumber compositions for cloud street and convective cell are calculated,respectively,on the basis of the atmospheric conditions at every stage.The distributions of vertical motions,convergent band and disturbed interface are obtained and compared with the cloud patterns in the convective processes. Thus the study seems to offer a likely explanation for the origin of large vortices in CBL.
基金supported by the National Natural Science Foundation of China (No. 51106006)
文摘The liquid droplet evaporation character is important for not only combustion chamber design process but also high-accuracy spray combustion simulation. In this paper, the suspended droplets＇ evaporation character was measured in a quiescent high-temperature environment by micro high-speed camera system. The gasoline and kerosene experimental results are consistent with the reference data. Methanol, common kerosene and aviation kerosene droplet evaporation characteristics, as well as their evaporation rate changing with temperature, were obtained. The evaporation rate experimental data were compared with the prediction result of Ranz-Marshall boiling temperature model（RMB）, Ranz-Marshall low-temperature model（RML）, drift flux model（DFM）, mass analogy model（MAM）, and stagnant film model（SFM）. The disparity between the experimental data and the model prediction results was mainly caused by the neglect of the natural convection effect, which was never introduced into the droplet evaporation concept. A new droplet evaporation model with consideration of natural convection buoyancy force effect was proposed in this paper. Under the experimental conditions in this paper, the calculation results of the new droplet evaporation model were agreed with the experimental data for kerosene, methanol and other fuels, with less than 20% relative deviations. The relative deviations between the new evaporation model predictions for kerosene and the experimental data from the references were within 10%.
